This invention relates to high-temperature adhesives and particularly to adhesives having excellent adhesive strength and high-temperature stability.
Polymide obtained by the reaction of tetracarboxylic dianhydride with diamine have known up to this time to have various outstanding properties and good high-temperature stability. Therefore polyimide is expected to develop a wide application in those fields which require stability at high temperatures.
A variety of polyimide has recently been developed and found a use also as adhesives. For example, in TOKKAISHO 58-157190 (1983), polymide derived from various diamines and tetracarboxylic dianhydrides is disclosed to have application to adhesive between a polyimide film and a copper foil in a flexible copper-clad circuit substrate.
Although polyimide adhesive is excellent in the high-temperature stability and adhesive strength, it is further required to be good in high-temperature flowability and easy to process at the time of adhesion.
Since traditional polyimide is generally poor in the light-transmittance and, in addition, has a tinge of brown, it has been unsatisfactory for use as the adhesives having a good transparency.
Therefore the object of this invention is to provide a novel polyimide adhesive having the high light-transmittance, good transparency, outstanding high-temperature flowability and excellent processability in addition to the ability of keeping adhesive strength during and after use at high temperatures.